62 MORPHOLOGY. _ 
wood) and Lignum Fernambuci (Brazil wood) arrive in commerce 
in the form of heartwood, freed from the colorless sapwood. In 
the case of Lignum Guaiaci, the valuable constituent, the resin, 
is also confined to the heartwood, although the dealers do not 
make a practice of removing the sapwood. 
In a botanical relation, the herbaceous stems (caulis) are dis- 
tinguished from the woody trunks (trunci), which, with the 
dicotyledons, as a rule, form branches (rami). 
Barks (Cortices). The organs of the stem, as well as 
roots, are invested with a bark, The monocotyledons do not 
possess a true bark, since they show no secondary growth in thick- 
ness. ‘The barks of dicotyledons—and such are officinal—con- 
sist in their young condition of a predominating parenchymatous 
tissue, derma, or primary bark, which is covered by the epider- 
mis. Only barks of several years’ growth, however, are brought 
into use, where the epidermis is replaced by cork. Where the 
latter is in a state of active growth, and represents a coherent 
layer, it is called periderm, outer bark, or exophleum." : 
Upon further development of the overground axes (or roots), 
which here come into consideration, the growth of the original 
bark is very soon increased through the activity of the cambium. 
Within the primary bark there is developed the secondary bark, 
inner bark, liber (bast), or endophlwum, the boundary of which 
is very frequently sharply defined from the primary bark. The 
bark then presents also a middle layer, the so-called middle bark 
_ or mesophleum,* which, at a later period, often becomes very 
neocon constituting the remainder of the primary 
- When, however, the formation of cork does not remain con 
fined to the periphery, but forms also in the interior of the 
bark tissue, the middle bark, by means of cork bands, ca) 
become entirely separated and thrown off, This process, the 
_ formation of bork or rhytidoma,’ can also extend to the inner 
bark. If, through peeling, the bork-scales themselves are als? 
' Ex, & out of, from, and ploror bark, 
* Mé6o5 middle, _ 
*"Puris, puridos fold, wrinkle; Scuda I build. 
